Effect of Water Temperature and Flow Rate on the Transmission of Microsporidial Gill Disease Caused by Loma salmonae in Rainbow Trout Oncorhynchus mykiss

Abstract

Two studies were designed to quantify the effect of water temperature and flow rate on the transmission potential of the important salmonid gill pathogen, Loma salmonae. Using survival analysis, increased water temperature and low flow rates were determined as risk factors for the transmission of microsporidial gill disease caused by L. salmonae in rainbow trout Oncorhynchus mykiss. Fish were experimentally infected with L. salmonae via a cohabitation exposure model and monitored for the development of branchial xenomas. On any given day, fish held at 11°C and 15°C had a hazard ratio equal to 0.80 and 0.68, respectively, for the development of branchial xenomas compared with fish held at 19°C. From the flow rate trial, fish housed in a low flow tank (0.83 L/min) had an increased chance of developing branchial xenomas when compared to fish in tanks at normal (1.67 L/min) and high (2.5 L/min) flow rates with hazard ratios reported as 0.69.